Taking over from Cristiano Ronaldo on United's right flank is an unenviable task. They are different players, but the Ecuadorian has brought his own qualities to the team.
"Antonio has settled very well. He's been terrific, the lad," Sir Alex said in his monthly column for Inside United magazine.
While Ronaldo was the major goal threat during his time as United's no.7, Valencia's strengths lie more in his ability to create opportunities for others - although his goals against CSKA Moscow and Bolton Wanderers are promising sign that he can contribute in that department as well.
But Sir Alex has chiefly been pleased with the service he provides from the wing.
"He's a good crosser of the ball," the United boss said. "He gets the ball in the box and gets it in from tight positions too. Very seldom are his crosses blocked, which isn't easy to do."